In the process of drilling oil and gas wells and recovering oil and gas from such wells, in many geological formations it is necessary to isolate the zone containing the oil and gas producing formation from the balance of the underground structure so as to prevent contamination of the oil and gas producing zone from salt water or other undersirable contaminants.
Historically this has been accomplished by the installation of packers in the well which expand to isolate the oil and gas producing zone and are placed above and below it or, if the producing zone is near the bottom of the well, it may only be necessary to place one packer above the producing zone. Such packers are based on mechanical means to set or retrieve the packer, which mechanical means in turn are actuated by the weight of the casing or by hydraulic force.
In the former case, the packer is set when shear pins which hold it away from the interior surface of the well bore are ruptured by the weight of the casing, thus forcing the packer to be compressed together and forcing a resilient section outward thereby sealing the production casing against either the outer casing or the well bore.
A common problem with the use of such mechanical actuated packers is that when the well bore is not straight or an obstruction is encountered the weight of the casing can shear the pins and set the packer prematurely.
This drawback is overcome in the second category of packers where the weight of the casing is not utilized to rupture shear pins but instead hydraulic pressure is used, which hydraulic pressure is applied to activate a mechanical device within the packer system in order to rupture the shear pins and thus set the packer in place.
Examples of this latter-type of packer are set forth in U.S. Pat. Nos. 3,239,008, Leutwyler, 3,374,838, Current, 4,018,272, Brown, et al., and 4,237,979, Weise. In each of these references hydraulic pressure is used to actuate a mechanical device which in turn permits the appropriate resilient member to be forced against the other casing or well bore. For example, in the case of U.S. Pat. No. 4,018,282, Brown, et al., hydraulic pressure in used to rupture shear pins which thus allow opposing portions of the packer to compress forcing a center rubber section outward, sealing against the outer casing or well bore. In U.S. Pat. No. 4,237,978, Weise, there are a series of slits which can be forced together when hydraulic pressure is applied which in turn forces a resilient device outward against the casing to function as a packer. In U.S. Pat. No. 3,374,838, Current, there are movable abutments which are expanded by hydraulic pressure. In all of the above examples there are mechanical parts within the packer which are activated by hydraulic pressure. All of these devices are complicated and thus relatively expensive because of the number of components which must be confined within a very small space. Furthermore, because of their complexity, these devices can malfunction very easily.